from math import sqrt
def is_prime(n):
    assert n > 0
    for factor in range(2,int(sqrt(n))+1):
        if n%factor == 0:
            return False
    return True if n != 1 else False

def main():
    filenames = ('a.txt','b.txt','c.txt')
    fs_list=[]
    try:
        for filename in filenames:
            fs_list.append(open(filename,'w',encoding='utf-8'))
        for number in range(1,10000):
            if is_prime(number):
                if number<100:
                    fs_list[0].write(str(number)+'\n')
                elif number <1000:
                    fs_list[1].write(str(number)+'\n')
                else:
                    fs_list[2].write(str(number)+'\n')
    except IOError as ex:
        print(ex)
        print('写文件时发生错误！')
    finally:
        for fs in fs_list:
            fs.close()
    print('操作完成')

if __name__=='__main__':
    main()